In order to study the forces maintaining the conformation of cytochrome c, a biologically active, three-fragment complex composed of heme fragment (1-25)H, and apofragments (28-38) and 56-104 was developed. This complex was obtained by a limited tryptic digestion of the parent complex formed by heme fragment (1-25)H and apofragments (1-65) and 39-104.